Lex retro non agit - "The law does not operate retroactively." A law cannot make something illegal that was legal at the time it was performed. See ex post facto law.⏎
Jura novit curia - "The court knows the law." Concept that parties to a case do not need to define how the law applies to their case. The court is solely responsible for determining what laws apply.⏎
Nemo dat quod non habet - [6] The basic rule that a person who does not own property (e.g. a thief) cannot confer it on another except with the true owner's authority (i.e. as his agent). Exceptions to this rule include sales under statutory powers, and cases where the doctrine of estoppel prevents a legal owner from denying a seller's right to sell.⏎
Nemo judex in sua causa - "No one shall be a judge in his own case." Prevents conflict of interest in courts. Often invoked when there is really no conflict, but when there is even the appearance of one.⏎
Nemo auditur propriam turpitudinem allegans - "No one can be heard, who invokes his own guilt." Nobody can bring a case that stems from their own illegal act.⏎